Wall wash lighting generally refers to light fittings used to illuminate a large area of wall surface. It is primarily used for external building wall illumination, scenery illumination, advertisement sign illumination, cultural facility illumination, and the like. In addition, it is also widely applied in atmospheric illumination at sites such as hotel lobbies, ballrooms and bars.
In recent years, LED wall wash lights have been widely applied at various sites, and the scope involved has also become increasingly broader, for example, from indoor to outdoor and from localized lighting to overall lighting. Moreover, wall wash lights are used at continuously enhanced and developed levels. If these recent trends continue, LED wall wash lights will likely develop into an indispensable portion of lighting engineering. It is expected that LED wall wash lights will develop into small, delicate and portable in volume, and will mainly be based on high-power LED light sources. Generally, LED wall wash lighting is implemented using a long bar (i.e., a “light bar”) having a plurality of LEDs mounted linearly in a plastic housing or the like.
For certain wall wash lighting applications, secondary optical lenses need to be provided for the LEDs to distribute the light beams according to certain desired characteristics. The design principle for secondary optical lenses are generally as follows: The total reflection collimating lens is first used to converge the light beams emitted from the LED to a very small light beam angle, and then the light beams are diffused at a wide-angle towards the wall surface through a line-shaped light distribution curved surface at the top of the lens, while very small light beam angle is unchanged in the direction perpendicular to the wall surface. As a result, most of the light beams can be gathered on the wall surface. One drawback of conventional secondary optical lenses, however, is that because the total reflection curved surface of the external face is smooth, when the fluorescent powder of the LED chip is not coated uniformly, the lenses can produced different color temperatures at different heights on the wall surface due to prism dispersion effects. For example, the color at lower heights on the wall surface adjacent to the LED light source tends to be slightly blue, while the color at higher wall heights tends to be slightly yellow. Accordingly, there is a need for an LED wall wash light lens that can mix light beams uniformly within a small angle to produce uniform illumination and consistent color temperature on the wall surface.